1. Field of the Invention
This invention relates to rotary compressors, and more particularly it is concerned with a through-vane type compressor, such as the one disclosed in Japanese Patent Publication No. 22201/76, suitable for use with a refrigerant compressor of an air conditioning system.
2. Description of the Prior Art
In a rotary compressor for use in compressing a refrigerant, the refrigerant contained in the working chambers of the compressor and the refrigerant supply and discharge lines tends to be condensed by the ambient temperature while the compressor is shut down, and this often leads to the refrigerant in a liquid state being stored in the working chambers and the refrigerant supply and discharge lines. Starting up of the compressor under these circumstances would result in the liquid refrigerant being compressed, and an inordinately high pressure would be produced in a working chamber in a compression stroke. Thus what is referred to as a sledging phenomenon would occur which would give rise to the problem of the vanes and the discharge valve being damaged and their service lives being shortened. To avoid this problem, proposals have been made to provide the compressor with a check valve mounted on an end plate attached to the housing which is adapted to be actuated when the pressure in the working chambers rises to an inordinately high level, as disclosed in Japanese Patent Publication No. 11725/62.
In case the compressor is suddenly started when a large volume of liquid is contained in a working chamber or the ambient temperature is relatively low, the sledging phenomenon would occur on a large scale, and an ordinary relief valve could not function satisfactorily as the check valve for avoiding damage to the vanes and valve. To increase the effectiveness of the check valve, attempts have been made to increase the diameter of the valve. However, the efficiency of the compressor would be reduced if the diameter of the valve exceeds the width of the vanes because the refrigerant being compressed would be blown through the check valve. A research conducted by inventors of the present application has revealed that even if the diameter of the check valve is slightly increased it is difficult to avoid compression of liquid refrigerant at all the rotational angles during one complete revolution of each vane.